Jose Mourinho's squad have made the worst start to a Premier League title defence since Blackburn in the 1995-96 season, after winning only once in their first four games.

Their 2-1 defeat at home to Crystal Palace on Saturday - just the second time Mourinho has lost a home league game with Chelsea - left them rooted in the bottom half of the table, eight points behind Manchester City.

Mourinho accused some of his players of failing to perform to the required consistency after that defeat and that view was endorsed by Neville, who suggested that the champions were struggling to match the intensity they showed in winning the title last season.

Speaking on Sky Sports, Neville said: "I'd be concerned now and the players need to give themselves a slap round the face.

"As a team, over a period of 12 months, they have built up trust with us as pundits but that could erode pretty quickly when you have a start to the season like this. Jose Mourinho needs to sort them out.

"We spoke about Manchester City last season, when they were champions, not being able to get themselves back up for it again. It's inexcusable that, to me.

"The idea that your desire wilts and moves in waves, like a rollercoaster. It can't happen. You have your summer off, you come back and you go again - and you have to put in the same amount of effort again.

"What makes you think that just because you've won the championship you can just relax and do things differently? And they are doing things differently.

"They're not behaving well as players in respect to their performances and they need to start playing like they can do."

Neville also questioned the fitness of several Chelsea players, and singled out Branislav Ivanovic - who endured a torried afternoon against Palace - for criticism.

"They look absolutely knackered - shot to pieces," he added. "You're watching someone who was probably the best right-back of last season in Ivanovic - he looks like he can't move out towards the ball. The tightness in relation to the four defenders just isn't there."

Neville's criticisms were echoed by his fellow Sky pundit and former Liverpool defender Jamie Carragher.

"That [defeat to Palace] was the first time I've thought it's a worry for Chelsea," he said. "It's like watching a team after they've come back from a World Cup - they're sluggish.

"But they've had a free summer, and I think this is the first time since Mourinho has been in our league where you're looking at his team and wondering what's going on?

"Mourinho doesn't lose matches, his teams don't concede goals - that's what is happening now. His teams don't always win everything but his teams are always out of the blocks quick. You can see it in the way they play. They're aggressive."